9 Public Service Indiana (PSI) is considering five possible locations to build power plants during the next 20 years. It will cost ci dollars to build a plant at site i and hi dollars to operate a site i plant for a year. A plant at site i can supply ki kilowatthours

(kwh) of generating capacity. During year t, dt kwh of generating capacity are required. Suppose that at most one plant can be built during a year, and if it is decided to build a plant at site i during year t, then the site i plant can be used to meet the year t (and later) generating requirements. Initially, PSI has 500,000 kwh of generating capacity available.

Formulate a recursion that PSI could use to minimize the sum of building and operating costs during the next 20 years.